The present invention relates to solid state image pick-up devices provided with an electronic shutter function, such as MOS-type and JFET-type solid state image pickup devices in which the picture elements in each accumulate charge representing an image signal.
Solid state image pickup devices, such as MOS-type and JFET-type image pickup devices, include an image sensor portion in which a plurality of picture elements are arranged in a two-dimensional matrix so that the picture elements are arranged both horizontally and vertically. Vertically aligned picture elements share a common vertical signal line. In operation, horizontal lines of picture elements are separately selected so that the charge accumulated in each element of the selected horizontal line is read via its corresponding vertical signal line. Typically, the read process is carried out by correlation double sampling (CDS) in which the charge accumulated in each picture element is first read, then the element is reset, and finally an "empty signal" is read from the element to be subtracted from the image signal read prior to the reset (termed a "read reset" herein). The empty signal is a black reference, and by subtracting the empty signal from the previously read image signal, the effect of a dark current level in the respective picture element is eliminated.
Conventional solid state imaging devices employ a first vertical scanning circuit coupled with the various horizontal lines of the image sensor portion on a first vertical side thereof through a plurality of respective drivers and switching transistors. The first vertical scanning circuit selects the horizontal lines in succession for reading. A second vertical scanning circuit is coupled with the horizontal lines at a second vertical side of the image sensor portion through a different respective plurality of drivers and switching transistors. The second vertical scanning circuit serves both to select the horizontal line which has also been selected by the first circuit for reading in order to reset the picture elements of that line between the reading of the image signal and the empty signal of each. The second vertical scanning circuit also applies a second reset signal to a second horizontal line spaced from the horizontal line being read by a predetermined number of lines. This second reset is termed an "electronic shutter" since after each of the elements has been reset by the second reset signal, it accumulates a charge proportional to an amount of light received thereby until such time that the line thus reset is again selected for reading.
In the conventional solid state image pickup device as described above, the impedance encountered during the read and reset of each horizontal line includes the on-resistance of both drivers as well as the on-resistance of both switching transistors on both sides of the line being read or reset. The relatively high level of impedance thus encountered limits the speed of operation of the image pickup device disadvantageously.